1. Field of the Invention
This invention relates to an electro-luminescence display (ELD), and more particularly to an ELD wherein a voltage supply line is divided into a plurality of voltage supply lines, and thereby reduce the number of pixels connected to each voltage supply line.
2. Description of the Related Art
An ELD is a device that is luminous by recombining electrons injected from an external source to a luminescent layer. The luminescent layer can be made from electro-luminescent (EL) materials with holes.
Because the ELD is luminous by the recombination of the injected electrons and holes, a back light is not required. This permits a display panel to be thinner and allows power consumption to remain low.
As a result, ELD has been the subject of growing interest in the field of displays. In particular, an organic ELD, in which the luminescent layer is formed from organic EL materials has received attention due to its advantages. The advantages include requiring a low driving voltage, having a high luminous efficiency, and allowing manufacture by a low temperature process.
typical active ELD has a number of scanning electrode lines crossing a number of data electrode lines. The ELD also includes a number of pixels, each of which is formed at the crossing. A voltage supply line is also supplied to each pixel, and the voltage supply lines are insulated from both the scanning electrode and data electrode lines. Each pixel includes a switching device comprising a thin film transistor (TFT), a driver, a storage capacitor, and an EL device.
FIG. 1 is a circuit diagram of a pixel array of a conventional ELD. In FIG. 1, the active matrix array has Mxc3x97N pixels 10, where M and N are integers. Each pixel 10 includes a switching transistor Qs, a driving transistor Qd, a capacitor C, and an EL device Ed.
A gate of the switching transistor Qs is connected to a scanning electrode line 12 and a source of Qs is connected to a data electrode line 14. A drain of Qs. is connected to a gate of the driving transistor Qd. A source of Qd is connected to a first voltage supply Vdd via a first power supply line 16, and a drain of Qd is connected to an anode of the EL device Ed.
A cathode of the EL device Ed is connected to a second voltage supply Vss via a second power supply line 18. It should be noted that all connections to Vss are common to all EL devices Ed. The EL device Ed includes at least one luminescent layer (not shown) made from an organic EL material, between the anode and the cathode.
Finally, the capacitor C is connected between the gate and the source of the driving transistor Qd as shown.
operation of the conventional ELD having the configuration as shown in FIG. 1 is as follows. A desired row of pixels is selected by applying a signal to a corresponding scanning electrode line 12. This applies a voltage to the gates of the desired switching transistors Qs to turn on the selected switching transistors Qs.
Then a desired pixel 10 is selected by applying a signal to a corresponding data electrode line 14. This applies a voltage to the gate of the desired driving transistor Qd to turn on the selected driving transistor Qs.
When the driving transistor is turned on, current is allowed to flow between the first and second voltage supplies Vdd and Vss through the EL device Ed. This in turn allows the EL device Ed to become luminous by the recombination of electrons and holes in the luminescent layer.
The capacitor C maintains the data signal level until the next time the data signal is applied.
FIG. 2 is a schematic diagram of the conventional ELD. The conventional ELD includes a pixel array 20, a data driving circuit 21, a gate driving circuit 23, first and second voltage supply terminals 25 and 27, and first and second power supply lines 29 and 31.
The pixel array 20 has the configuration as shown in FIG. 1. The array 20 is arranged to be electrically connected to the data driving circuit 21 and the gate driving circuit 23 at the periphery thereof (not shown). The data driving circuit 21 and the gate driving circuit 23 are connected to the data electrode lines 14 and the scanning electrode lines 12, respectively, which are in turn connected to the pixel array 20, as shown in FIG. 1.
The first and second voltage supplies Vdd and Vss are applied to the first and second voltage supply terminals 25 and 27, respectively, which are in turn connected to the first and second power supply lines 29 and 31, respectively, as shown in FIG. 2. And as shown in FIG. 1, the first and second power supply lines are connected to each pixel 10 of the pixel array 20. It should be noted again that the cathodes of EL devices Ed serve as a common electrode.
When a particular pixel 10 of the conventional ELD is driven, the pixel 10 receives the first and second supply voltages Vdd and Vss through the first and second voltage supply terminals 25 and 27, respectively. As a result, current flows through the first and second power supply lines 29 and 31, again respectively. Only a minute amount of current is required to make the pixel 10 luminous.
However, the conventional ELD suffers from at least the following problem. Even though each pixel requires a small amount of current, the sum of current required to drive all pixels can be significant. It can be significant enough to generate significant amounts of heat and thus to melt the supply lines and damage the luminescent layers of the pixels. In both cases, the reliability of the ELD is compromised. This problem becomes more acute as the ELD becomes larger and as the resolution of the display is increased.
Accordingly, is an object of the present invention to provide an electro-luminescence display capable of preventing or minimizing heat generation caused by a current flowing through the first and second power supply lines, and thereby improve its reliability.
To achieve these and other objects of the invention, an electro-luminescence display according to an embodiment of the present invention includes a pixel array having a number of pixels. Each pixel includes an electro-luminescence device having a luminescent layer made from an electro-luminescent material. The electro-luminescence device also includes an anode electrode and a cathode electrode serving as a common electrode for the ELD. The ELD may be an active matrix type.
The display also includes a gate driving circuit and the data driving circuit, being connected, via a plurality of scanning electrode lines and a plurality of data electrode lines, respectively, to the pixel array, to selectively drive each pixel.
The display further includes first and second voltage supply terminals to which first and second supply voltages are applied, from an external circuit for example. First and second power supply lines couple the first and second voltage supply terminals with the pixel array.
Each first power supply line supplies a subset of the pixels with the first supply voltage. Likewise, each second power supply line supplies another subset of the pixels with the second supply voltage.